1. Field of the Invention
The present invention relates to an immobilization device which is provided to cover at least a part of a patient's body that needs to be immobilized and/or supported, the immobilization device being at least partly made of a plastic material.
2. The Prior Art
Immobilization and adaptation devices are frequently used in orthopedic applications, in the immobilization of inflamed or injured joints in case of trauma or diseases, for the support and immobilization of ligaments and muscular structures and in physical rehabilitation applications, and in podiatry, for example, as insole (foot-bed) applications.
Immobilization devices also know a wide use in radiation therapy and diagnostic imaging. Especially in diagnostic imaging and radiation therapy, proper immobilization and reproducible positioning of the part of the patient's body to be treated with respect to the radiation source is of vital importance. In radiation therapy it is a prerequisite to ensure that the radiation is delivered exactly at the target position where it is needed, while minimizing the risk to exposure of surrounding healthy tissue. Reproducible positioning is of utmost relevance in fractionated treatment, where a radiation dose is divided into a multiplicity of sub doses which are delivered to the patient at different directions and on different points in time, to allow for a maximum recovery of healthy tissue and to minimize complicat ions from overexposure to radiation. To simultaneously achieve reproducible positioning and limit the possibility of displacing the body part in the course of the treatment, the position of the body part is fixed using a immobilization device which is moulded to correspond as accurate as possible to the shape of the body part.
In the art a wide variety of plastic materials has been used in the casting of orthopaedic structures, rehabilitation technique aids, radiation therapy fixation and imaging fixation. However, only a few of these known materials are suitable for direct moulding to the patients' body because of their low melting temperature and good mouldability and elasticity in the molten state. The majority of the engineering plastics have a melting temperature which is above 100° C. These materials may be suitable for use in immobilisation structures as well, provided they are moulded to a positive mould corresponding to the part of the patients' body that needs immobilisation. The use of such materials however involves the additional step of making the positive mould.
A plurality of existing techniques is disclosed in U.S. Pat. No. 5,584,800. A first disclosed technique in which a knit fibre glass fabric is impregnated with a polyurethane resin, presents the disadvantages that fibre glass insufficiently adapts to the fine structure of the body and besides this often obstructs x-rays, thus interfering with the x-ray image. Polyester fabrics used in stead of glass fibre fabric show an inferior strength-to-weight ratio. According to the noted patent, other known fixation devices are made of a thermoplastic material, which is heated to a temperature above its softening point and than moulded over the body part to be immobilized, to provide the best fit to this body part. The use of thermoplastic material ensures that optimal adaptation of the fixation device to the body part involved may be achieved.
The inventor has however observed that with an immobilisation device made of one single thermoplastic material, the stability of the device is still insufficient and provides insufficient guarantee that the displaceability of the body part is restrained to less than 0.5 to one or a few mm. This has the consequence that adjusting the patient positioning is insufficiently accurate as well as the reproducibility of the patient positioning.
Still other known immobilisation devices are made of plastic material with higher melting temperatures, e.g. polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC) which is moulded into a standard shape, and made available in a single size or a few sizes. To allow some adaptation to the body part and to provide for an improved fit, the device comprises for example Velcro® strips, with which parts of the device may be pulled towards each other and releasably fixed in that position. These immobilisation devices however present insufficient fit and insufficient comfort. The insufficient fit entails the risk that the immobilisation provided is insufficiently adequate and accurate.
There is thus a need to an immobilisation device the shape of which shows an improved adaptability to the body part that needs immobilisation and to the position in which the body part is to be immobilised.
It is therefore the aim of the present invention to provide an immobilisation device which is suitable for use in a wide variety of applications, for example orthopaedics, physical rehabilitation, diagnostic imaging and radiation therapy and podiatry. It is further the aim of the present invention to provide an immobilisation device which shows an improved adaptability to the body part that needs immobilisation and to the position in which the body part is to be immobilised.